Methods and apparatus of video coding for triangle prediction

ABSTRACT

Methods and apparatuses are provided for video coding. The method includes: partitioning video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs) including at least one triangular shaped PU; constructing a first merge list including a plurality of candidates, each including one or more motion vectors, based on a merge list construction process for regular merge prediction; and obtaining an index listing including a plurality of reference indices, where each reference index comprises a reference to a motion vector of a candidate in the first merge list.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationNo. 62/817,537, entitled “Video Coding with Triangle Prediction” filedon Mar. 12, 2019, and U.S. Provisional Application No. 62/817,852,entitled “Video Coding with Triangle Prediction” filed on Mar. 13, 2019,both of which are incorporated by reference in their entirety for allpurpose.

FIELD

The present application generally relates to video coding andcompression, and in particular but not limited to, methods and apparatusfor motion compensated prediction using triangular prediction unit (i.e.a special case of geometric partition prediction unit) in video coding.

BACKGROUND

Digital video is supported by a variety of electronic devices, such asdigital televisions, laptop or desktop computers, tablet computers,digital cameras, digital recording devices, digital media players, videogaming consoles, smart phones, video teleconferencing devices, videostreaming devices, etc. The electronic devices transmit, receive,encode, decode, and/or store digital video data by implementing videocompression/decompression. Digital video devices implement video codingtechniques, such as those described in the standards defined byVersatile Video Coding (VVC), Joint Exploration Test Model (JEM),MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards.

Video coding generally utilizes prediction methods (e.g.,inter-prediction, intra-prediction) that take advantage of redundancypresent in video images or sequences. An important goal of video codingtechniques is to compress video data into a form that uses a lower bitrate, while avoiding or minimizing degradations to video quality. Withever-evolving video services becoming available, encoding techniqueswith better coding efficiency are needed.

Video compression typically includes performing spatial (intra frame)prediction and/or temporal (inter frame) prediction to reduce or removeredundancy inherent in the video data. For block-based video coding, avideo frame is partitioned into one or more slices, each slice havingmultiple video blocks, which may also be referred to as coding treeunits (CTUs). Each CTU may contain one coding unit (CU) or recursivelysplit into smaller CUs until the predefined minimum CU size is reached.Each CU (also named leaf CU) contains one or multiple transform units(TUs) and each CU also contains one or multiple prediction units (PUs).Each CU can be coded in intra, inter or IBC modes. Video blocks in anintra coded (I) slice of a video frame are encoded using spatialprediction with respect to reference samples in neighbor blocks withinthe same video frame. Video blocks in an inter coded (P or B) slice of avideo frame may use spatial prediction with respect to reference samplesin neighbor blocks within the same video frame or temporal predictionwith respect to reference samples in other previous and/or futurereference video frames.

Spatial or temporal prediction based on a reference block that has beenpreviously encoded, e.g., a neighbor block, results in a predictiveblock for a current video block to be coded. The process of finding thereference block may be accomplished by block matching algorithm.Residual data representing pixel differences between the current blockto be coded and the predictive block is referred to as a residual blockor prediction errors. An inter-coded block is encoded according to amotion vector that points to a reference block in a reference frameforming the predictive block, and the residual block. The process ofdetermining the motion vector is typically referred to as motionestimation. An intra coded block is encoded according to an intraprediction mode and the residual block. For further compression, theresidual block is transformed from the pixel domain to a transformdomain, e.g., frequency domain, resulting in residual transformcoefficients, which may then be quantized. The quantized transformcoefficients, initially arranged in a two-dimensional array, may bescanned to produce a one-dimensional vector of transform coefficients,and then entropy encoded into a video bitstream to achieve even morecompression.

The encoded video bitstream is then saved in a computer-readable storagemedium (e.g., flash memory) to be accessed by another electronic devicewith digital video capability or directly transmitted to the electronicdevice wired or wirelessly. The electronic device then performs videodecompression (which is an opposite process to the video compressiondescribed above) by, e.g., parsing the encoded video bitstream to obtainsyntax elements from the bitstream and reconstructing the digital videodata to its original format from the encoded video bitstream based atleast in part on the syntax elements obtained from the bitstream, andrenders the reconstructed digital video data on a display of theelectronic device.

With digital video quality going from high definition, to 4K×2K or even8K×4K, the amount of vide data to be encoded/decoded growsexponentially. It is a constant challenge in terms of how the video datacan be encoded/decoded more efficiently while maintaining the imagequality of the decoded video data.

In a Joint Video Experts Team (JVET) meeting, JVET defined the firstdraft of Versatile Video Coding (VVC) and the VVC Test Model 1 (VTM1)encoding method. It was decided to include a quadtree with nestedmulti-type tree using binary and ternary splits coding block structureas the initial new coding feature of VVC. Since then, the referencesoftware VTM to implement the encoding method and the draft VVC decodingprocess has been developed during the JVET meetings.

SUMMARY

In general, this disclosure describes examples of techniques relating tomotion compensated prediction using triangular prediction unit, which isa special case of geometric partition prediction, in video coding.

According to a first aspect of the present disclosure, there is provideda method for video coding, including: partitioning video pictures into aplurality of coding units (CUs), at least one of which is furtherpartitioned into two prediction units (PUs) including at least onetriangular shaped PU; constructing a first merge list including aplurality of candidates, each including one or more motion vectors,based on a merge list construction process for regular merge prediction;and obtaining an index listing including a plurality of referenceindices, where each reference index includes a reference to a motionvector of a candidate in the first merge list.

According to a second aspect of the present disclosure, there isprovided an apparatus for video coding, including: one or moreprocessors and a memory configured to store instructions executable bythe one or more processors. The one or more processors, upon executionof the instructions, are configured to: partition video pictures into aplurality of coding units (CUs), at least one of which is furtherpartitioned into two prediction units (PUs) including at least onetriangular shaped PU; construct a first merge list including a pluralityof candidates, each including one or more motion vectors, based on amerge list construction process for regular merge prediction; and obtainan index listing including a plurality of reference indices, where eachreference index includes a reference to a motion vector of a candidatein the first merge list.

According to a third aspect of the present disclosure, there is providedanon-transitory computer readable storage medium, including instructionsstored therein. Upon execution of the instructions by one or moreprocessors, the instructions cause the one or more processors to:partition video pictures into a plurality of coding units (CUs), atleast one of which is further portioned into two prediction units (PUs)including at least one triangular shaped PU; construct a first mergelist including a plurality of candidates, each including one or moremotion vectors, based on a merge list construction process for regularmerge prediction; and obtain an index listing including a plurality ofreference indices, where each reference index includes a reference to amotion vector of a candidate in the first merge list.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the examples of the present disclosurewill be rendered by reference to specific examples illustrated in theappended drawings. Given that these drawings depict only some examplesand are not therefore considered to be limiting in scope, the exampleswill be described and explained with additional specificity and detailsthrough the use of the accompanying drawings.

FIG. 1 is a block diagram illustrating an exemplary video encoder inaccordance with some implementations of the present disclosure.

FIG. 2 is a block diagram illustrating an exemplary video decoder inaccordance with some implementations of the present disclosure.

FIG. 3 is a schematic diagram illustrating a quadtree plus binary tree(QTBT) structure in accordance with some implementations of the presentdisclosure.

FIG. 4 is a schematic diagram illustrating an example of a picturedivided into CTUs in accordance with some implementations of the presentdisclosure.

FIG. 5 is a schematic diagram illustrating multi-type tree splittingmodes in accordance with some implementations of the present disclosure.

FIG. 6 is a schematic diagram illustrating splitting a CU intotriangular prediction units in accordance with some implementations ofthe present disclosure.

FIG. 7 is a schematic diagram illustrating positions of neighboringblocks in accordance with some implementations of the presentdisclosure.

FIG. 8 is a schematic diagram illustrating positions of spatial mergecandidates in accordance with some implementations of the presentdisclosure.

FIG. 9 is a schematic diagram illustrating motion vector scaling for atemporal merge candidate in accordance with some implementations of thepresent disclosure.

FIG. 10 is a schematic diagram illustrating candidate positions for atemporal merge candidate in accordance with some implementations of thepresent disclosure.

FIG. 11A to FIG. 11B are schematic diagrams illustrating examples ofuni-prediction motion vector (MV) selection for triangle prediction modein accordance with some implementations of the present disclosure.

FIG. 12A to FIG. 12D are schematic diagrams illustrating examples ofuni-prediction MV selection for triangle prediction mode in accordancewith some implementations of the present disclosure.

FIG. 13 is a block diagram illustrating an exemplary apparatus for videocoding in accordance with some implementations of the presentdisclosure.

FIG. 14 is a flowchart illustrating an exemplary process of video codingfor motion compensated prediction using triangular prediction unit inaccordance with some implementations of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to specific implementations,examples of which are illustrated in the accompanying drawings. In thefollowing detailed description, numerous non-limiting specific detailsare set forth in order to assist in understanding the subject matterpresented herein. But it will be apparent to one of ordinary skill inthe art that various alternatives may be used. For example, it will beapparent to one of ordinary skill in the art that the subject matterpresented herein can be implemented on many types of electronic deviceswith digital video capabilities.

Reference throughout this specification to “one embodiment,” “anembodiment,” “an example,” “some embodiments,” “some examples,” orsimilar language means that a particular feature, structure, orcharacteristic described is included in at least one embodiment orexample. Features, structures, elements, or characteristics described inconnection with one or some embodiments are also applicable to otherembodiments, unless expressly specified otherwise.

Throughout the disclosure, the terms “first,” “second,” “third,” andetc. are all used as nomenclature only for references to relevantelements, e.g. devices, components, compositions, steps, and etc.,without implying any spatial or chronological orders, unless expresslyspecified otherwise. For example, a “first device” and a “second device”may refer to two separately formed devices, or two parts, components oroperational states of a same device, and may be named arbitrarily.

As used herein, the term “if” or “when” may be understood to mean “upon”or “in response to” depending on the context. These terms, if appear ina claim, may not indicate that the relevant limitations or features areconditional or optional.

The terms “module,” “sub-module,” “circuit,” “sub-circuit,” “circuitry,”“sub-circuitry,” “unit,” or “sub-unit” may include memory (shared,dedicated, or group) that stores code or instructions that can beexecuted by one or more processors. A module may include one or morecircuits with or without stored code or instructions. The module orcircuit may include one or more components that are directly orindirectly connected. These components may or may not be physicallyattached to, or located adjacent to, one another.

A unit or module may be implemented purely by software, purely byhardware, or by a combination of hardware and software. In a puresoftware implementation, for example, the unit or module may includefunctionally related code blocks or software components, that aredirectly or indirectly linked together, so as to perform a particularfunction.

FIG. 1 shows a block diagram illustrating an exemplary block-basedhybrid video encoder 100 which may be used in conjunction with manyvideo coding standards using block-based processing. In the encoder 100,a video frame is partitioned into a plurality of video blocks forprocessing. For each given video block, a prediction is formed based oneither an inter prediction approach or an intra prediction approach. Ininter prediction, one or more predictors are formed through motionestimation and motion compensation, based on pixels from previouslyreconstructed frames. In intra prediction, predictors are formed basedon reconstructed pixels in a current frame. Through mode decision, abest predictor may be chosen to predict a current block.

A prediction residual, representing the difference between a currentvideo block and its predictor, is sent to a Transform circuitry 102.Transform coefficients are then sent from the Transform circuitry 102 toa Quantization circuitry 104 for entropy reduction. Quantizedcoefficients are then fed to an Entropy Coding circuitry 106 to generatea compressed video bitstream. As shown in FIG. 1, prediction-relatedinformation 110 from an inter prediction circuitry and/or an IntraPrediction circuitry 112, such as video block partition info, motionvectors, reference picture index, and intra prediction mode, are alsofed through the Entropy Coding circuitry 106 and saved into a compressedvideo bitstream 114.

In the encoder 100, decoder-related circuitries are also needed in orderto reconstruct pixels for the purpose of prediction. First, a predictionresidual is reconstructed through an Inverse Quantization 116 and anInverse Transform circuitry 118. This reconstructed prediction residualis combined with a Block Predictor 120 to generate un-filteredreconstructed pixels for a current video block.

Spatial prediction (or “intra prediction”) uses pixels from samples ofalready coded neighboring blocks (which are called reference samples) inthe same video frame as the current video block to predict the currentvideo block.

Temporal prediction (also referred to as “inter prediction”) usesreconstructed pixels from already-coded video pictures to predict thecurrent video block. Temporal prediction reduces temporal redundancyinherent in the video signal. Temporal prediction signal for a givencoding unit (CU) or coding block is usually signaled by one or moremotion vectors (MVs) which indicate the amount and the direction ofmotion between the current CU and its temporal reference. Further, ifmultiple reference pictures are supported, one reference picture indexis additionally sent, which is used to identify from which referencepicture in the reference picture store the temporal prediction signalcomes.

After spatial and/or temporal prediction is performed, an intra/intermode decision circuitry 121 in the encoder 100 chooses the bestprediction mode, for example based on the rate-distortion optimizationmethod. The block predictor 120 is then subtracted from the currentvideo block; and the resulting prediction residual is de-correlatedusing the transform circuitry 102 and the quantization circuitry 104.The resulting quantized residual coefficients are inverse quantized bythe inverse quantization circuitry 116 and inverse transformed by theinverse transform circuitry 118 to form the reconstructed residual,which is then added back to the prediction block to form thereconstructed signal of the CU. Further in-loop filtering 115, such as adeblocking filter, a sample adaptive offset (SAO), and/or an adaptivein-loop filter (ALF) may be applied on the reconstructed CU before it isput in the reference picture store of the picture buffer 117 and used tocode future video blocks. To form the output video bitstream 114, codingmode (inter or intra), prediction mode information, motion information,and quantized residual coefficients are all sent to the entropy codingunit 106 to be further compressed and packed to form the bit-stream.

For example, a deblocking filter is available in AVC, HEVC as well asthe now-current version of VVC. In HEVC, an additional in-loop filtercalled SAO (sample adaptive offset) is defined to further improve codingefficiency. In the now-current version of the VVC standard, yet anotherin-loop filter called ALF (adaptive loop filter) is being activelyinvestigated, and it has a good chance of being included in the finalstandard.

These in-loop filter operations are optional. Performing theseoperations helps to improve coding efficiency and visual quality. Theymay also be turned off as a decision rendered by the encoder 100 to savecomputational complexity.

It should be noted that intra prediction is usually based on unfilteredreconstructed pixels, while inter prediction is based on filteredreconstructed pixels if these filter options are turned on by theencoder 100.

FIG. 2 is a block diagram illustrating an exemplary block-based videodecoder 200 which may be used in conjunction with many video codingstandards. This decoder 200 is similar to the reconstruction-relatedsection residing in the encoder 100 of FIG. 1. In the decoder 200, anincoming video bitstream 201 is first decoded through an EntropyDecoding 202 to derive quantized coefficient levels andprediction-related information. The quantized coefficient levels arethen processed through an Inverse Quantization 204 and an InverseTransform 206 to obtain a reconstructed prediction residual. A blockpredictor mechanism, implemented in an Intra/inter Mode Selector 212, isconfigured to perform either an Intra Prediction 208, or a MotionCompensation 210, based on decoded prediction information. A set ofunfiltered reconstructed pixels are obtained by summing up thereconstructed prediction residual from the Inverse Transform 206 and apredictive output generated by the block predictor mechanism, using asummer 214.

The reconstructed block may further go through an In-Loop Filter 209before it is stored in a Picture Buffer 213 which functions as areference picture store. The reconstructed video in the Picture Buffer213 may be sent to drive a display device, as well as used to predictfuture video blocks. In situations where the In-Loop Filter 209 isturned on, a filtering operation is performed on these reconstructedpixels to derive a final reconstructed Video Output 222.

Video coding/decoding standards mentioned above, such as VVC, JEM, HEVC,MPEG-4, Part 10, are conceptually similar. For example, they all useblock-based processing. Block partitioning schemes in some standards areelaborated below.

HEVC is based on a hybrid block-based motion-compensated transformcoding architecture. The basic unit for compression is termed codingtree unit (CTU). The maximum CTU size is defined as up to 64 by 64 lumapixels, and two blocks of 32 by 32 chroma pixels for 4:2:0 chromaformat. Each CTU may contain one coding unit (CU) or recursively splitinto four smaller CUs until the predefined minimum CU size is reached.Each CU (also named leaf CU) contains one or multiple prediction units(PUs) and a tree of transform units (TUs).

In general, except for monochrome content, a CTU may include one lumacoding tree block (CTB) and two corresponding chroma CTBs; a CU mayinclude one luma coding block (CB) and two corresponding chroma CBs; aPU may include one luma prediction block (PB) and two correspondingchroma PBs; and a TU may include one luma transform block (TB) and twocorresponding chroma TBs. However, exceptions may occur because theminimum TB size is 4×4 for both luma and chroma (i.e., no 2×2 chroma TBis supported for 4:2:0 color format) and each intra chroma CB always hasonly one intra chroma PB regardless of the number of intra luma PBs inthe corresponding intra luma CB.

For an intra CU, the luma CB can be predicted by one or four luma PBs,and each of the two chroma CBs is always predicted by one chroma PB,where each luma PB has one intra luma prediction mode and the two chromaPBs share one intra chroma prediction mode. Moreover, for the intra CU,the TB size cannot be larger than the PB size. In each PB, the intraprediction is applied to predict samples of each TB inside the PB fromneighboring reconstructed samples of the TB. For each PB, in addition to33 directional intra prediction modes, DC and planar modes are alsosupported to predict flat regions and gradually varying regions,respectively.

For each inter PU, one of three prediction modes including inter, skip,and merge, may be selected. Generally speaking, a motion vectorcompetition (MVC) scheme is introduced to select a motion candidate froma given candidate set that includes spatial and temporal motioncandidates. Multiple references to the motion estimation allow findingthe best reference in 2 possible reconstructed reference picture lists(namely List 0 and List 1). For the inter mode (termed AMVP mode, whereAMVP stands for advanced motion vector prediction), inter predictionindicators (List 0, List 1, or bi-directional prediction), referenceindices, motion candidate indices, motion vector differences (MVDs) andprediction residual are transmitted. As for the skip mode and the mergemode, only merge indices are transmitted, and the current PU inheritsthe inter prediction indicator, reference indices, and motion vectorsfrom a neighboring PU referred by the coded merge index. In the case ofa skip coded CU, the residual signal is also omitted.

The Joint Exploration Test Model (JEM) is built up on top of the HEVCtest model. The basic encoding and decoding flowchart of HEVC is keptunchanged in the JEM; however, the design elements of most importantmodules, including the modules of block structure, intra and interprediction, residue transform, loop filter and entropy coding, aresomewhat modified and additional coding tools are added. The followingnew coding features are included in the JEM.

In HEVC, a CTU is split into CUs by using a quadtree structure denotedas coding tree to adapt to various local characteristics. The decisionwhether to code a picture area using inter-picture (temporal) orintra-picture (spatial) prediction is made at the CU level. Each CU canbe further split into one, two or four PUs according to the PU splittingtype. Inside one PU, the same prediction process is applied and therelevant information is transmitted to the decoder on a PU basis. Afterobtaining the residual block by applying the prediction process based onthe PU splitting type, a CU can be partitioned into transform units(TUs) according to another quadtree structure similar to the coding treefor the CU. One of key features of the HEVC structure is that it has themultiple partition conceptions including CU, PU, and TU.

FIG. 3 is a schematic diagram illustrating a quadtree plus binary tree(QTBT) structure in accordance with some implementations of the presentdisclosure.

The QTBT structure removes the concepts of multiple partition types,i.e., it removes the separation of the CU, PU and TU concepts, andsupports more flexibility for CU partition shapes. In the QTBT blockstructure, a CU may have either a square or rectangular shape. As shownin FIG. 3, a coding tree unit (CTU) is first partitioned by a quaternarytree (i.e., quadtree) structure. The quadtree leaf nodes may be furtherpartitioned by a binary tree structure. There are two splitting types inthe binary tree splitting: symmetric horizontal splitting and symmetricvertical splitting. The binary tree leaf nodes are called coding units(CUs), and that segmentation is used for prediction and transformprocessing without any further partitioning. This means that the CU, PUand TU have the same block size in the QTBT coding block structure. Inthe JEM, a CU sometimes consists of coding blocks (CBs) of differentcolour components, e.g., one CU contains one luma CB and two chroma CBsin the case of P and B slices of the 4:2:0 chroma format, and sometimesconsists of a CB of a single component, e.g., one CU contains only oneluma CB or just two chroma CBs in the case of I slices.

The following parameters are defined for the QTBT partitioning scheme.

-   -   CTU size: the root node size of a quadtree, the same concept as        in the HEVC;    -   MinQTSize: the minimum allowed quadtree leaf node size;    -   MaxBTSize: the maximum allowed binary tree root node size;    -   MaxBTDepth: the maximum allowed binary tree depth;    -   MinBTSize: the minimum allowed binary tree leaf node size.

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 luma samples with two corresponding 64×64 blocks of chromasamples (with a 4:2:0 chroma format), the MinQTSize is set as 16×16, theMaxBTSize is set as 64×64, the MinBTSize (for both width and height) isset as 4×4, and the MaxBTDepth is set as 4. The quadtree partitioning isapplied to the CTU first to generate quadtree leaf nodes. The quadtreeleaf nodes may have a size from 16×16 (i.e., the MinQTSize) to 128×128(i.e., the CTU size). If the quadtree leaf node is 128×128, it will notbe further split by the binary tree since the size exceeds the MaxBTSize(i.e., 64×64). Otherwise, the quadtree leaf node could be furtherpartitioned by the binary tree. Therefore, the quadtree leaf node isalso the root node for the binary tree and it has the binary tree depthas 0. When the binary tree depth reaches MaxBTDepth (i.e., 4), nofurther splitting is considered. When the binary tree node has a widthequal to MinBTSize (i.e., 4), no further horizontal splitting isconsidered. Similarly, when the binary tree node has a height equal toMinBTSize, no further vertical splitting is considered. The leaf nodesof the binary tree are further processed by prediction and transformprocessing without any further partitioning. In the JEM, the maximum CTUsize is 256×256 luma samples.

An example of block partitioning by using the QTBT scheme, and thecorresponding tree representation are illustrated in FIG. 3. The solidlines indicate quadtree splitting and dotted lines indicate binary treesplitting. As shown in FIG. 3, the coding tree unit (CTU) 300 is firstpartitioned by a quadtree structure, and three of the four quadtree leafnodes 302, 304, 306, 308 are further partitioned by either a quadtreestructure or a binary tree structure. For example, the quadtree leafnode 306 is further partitioned by quadtree splitting; the quadtree leafnode 304 is further partitioned into two leaf nodes 304 a, 304 b bybinary tree splitting; and the quadtree leaf node 302 is also furtherpartitioned by binary tree splitting. In each splitting (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting. For example,for the quadtree leaf node 304, 0 is signaled to indicate horizontalsplitting, and for the quadtree leaf node 302, 1 is signaled to indicatevertical splitting. For quadtree splitting, there is no need to indicatethe splitting type since quadtree splitting always splits a block bothhorizontally and vertically to produce 4 sub-blocks with an equal size.

In addition, the QTBT scheme supports the ability for the luma andchroma to have a separate QTBT structure. Currently, for P and B slices,the luma and chroma CTBs in one CTU share the same QTBT structure.However, for I slices, the luma CTB is partitioned into CUs by a QTBTstructure, and the chroma CTBs are partitioned into chroma CUs byanother QTBT structure. This means that a CU in an I slice consists of acoding block of the luma component or coding blocks of two chromacomponents, and a CU in a P or B slice consists of coding blocks of allthree colour components.

In a Joint Video Experts Team (JVET) meeting, the JVET defined the firstdraft of the Versatile Video Coding (VVC) and the VVC Test Model 1(VTM1) encoding method. It was decided to include a quadtree with nestedmulti-type tree using binary and ternary splits coding block structureas the initial new coding feature of VVC.

In VVC, the picture partitioning structure divides the input video intoblocks called coding tree units (CTUs). A CTU is split using a quadtreewith nested multi-type tree structure into coding units (CUs), with aleaf coding unit (CU) defining a region sharing the same prediction mode(e.g. intra or inter). Here, the term “unit” defines a region of animage covering all components; the term “block” is used to define aregion covering a particular component (e.g. luma), and may differ inspatial location when considering the chroma sampling format such as4:2:0.

Partitioning of the Picture into CTUs

FIG. 4 is a schematic diagram illustrating an example of a picturedivided into CTUs in accordance with some implementations of the presentdisclosure.

In VVC, pictures are divided into a sequence of CTUs, and the CTUconcept is the same as that of the HEVC. For a picture that has threesample arrays, a CTU consists of an N×N block of luma samples togetherwith two corresponding blocks of chroma samples. FIG. 4 shows theexample of a picture 400 divided into CTUs 402.

The maximum allowed size of the luma block in a CTU is specified to be128×128 (although the maximum size of the luma transform blocks is64×64).

Partitioning of the CTUs Using a Tree Structure

FIG. 5 is a schematic diagram illustrating multi-type tree splittingmodes in accordance with some implementations of the present disclosure.

In HEVC, a CTU is split into CUs by using a quaternary-tree structuredenoted as coding tree to adapt to various local characteristics. Thedecision whether to code a picture area using inter-picture (temporal)or intra-picture (spatial) prediction is made at the leaf CU level. Eachleaf CU can be further split into one, two or four PUs according to thePU splitting type. Inside one PU, the same prediction process isapplied, and the relevant information is transmitted to the decoder on aPU basis. After obtaining the residual block by applying the predictionprocess based on the PU splitting type, a leaf CU can be partitionedinto transform units (TUs) according to another quaternary-treestructure similar to the coding tree for the CU. One of key feature ofthe HEVC structure is that it has the multiple partition conceptionsincluding CU, PU, and TU.

In VVC, a quadtree with nested multi-type tree using binary and ternarysplits segmentation structure replaces the concepts of multiplepartition unit types, i.e. it removes the separation of the CU, PU andTU concepts except as needed for CUs that have a size too large for themaximum transform length, and supports more flexibility for CU partitionshapes. In the coding tree structure, a CU may have either a square orrectangular shape. A coding tree unit (CTU) is first partitioned by aquaternary tree (i.e., quadtree) structure. Then the quaternary treeleaf nodes can be further partitioned by a multi-type tree structure. Asshown in FIG. 5, there are four splitting types in multi-type treestructure: vertical binary splitting 502 (SPLIT_BT_VER), horizontalbinary splitting 504 (SPLIT_BT_HOR), vertical ternary splitting 506(SPLIT_TT_VER), and horizontal ternary splitting 508 (SPLIT_TT_HOR). Themulti-type tree leaf nodes are called coding units (CUs), and unless theCU is too large for the maximum transform length, this segmentation isused for prediction and transform processing without any furtherpartitioning. This means that, in most cases, the CU, PU and TU have thesame block size in the quadtree with nested multi-type tree coding blockstructure. The exception occurs when the maximum supported transformlength is smaller than the width or height of the color component of theCU. In VTM1, a CU consists of coding blocks (CBs) of different colorcomponents, e.g., one CU contains one luma CB and two chroma CBs (unlessthe video is monochrome, i.e., having only one color component).

Partitioning CUs into Multiple Prediction Units

In VVC, for each CU partitioned based on the structure illustratedabove, prediction of the block content can be performed either on thewhole CU block or in a sub-block manner explained in the followingparagraphs. The operation unit of such prediction is called predictionunit (or PU).

In the case of intra prediction (or intra-frame prediction), usually thesize of the PU is equal to the size of the CU. In other words, theprediction is performed on the whole CU block. For inter prediction (orinter-frame prediction), the size of the PU can be equal or less thanthe size of the CU. In other words, there are cases where a CU may besplit into multiple PUs for prediction.

Some examples of having the PU size smaller than the CU size include anaffine prediction mode, an Advanced Temporal Level Motion VectorPrediction (ATMVP) mode, and a triangle prediction mode, etc.

Under the affine prediction mode, a CU may be split into multiple 4×4PUs for prediction. Motion vectors can be derived for each 4×4 PU andmotion compensation can be performed accordingly on the 4×4 PU. Underthe ATMVP mode, a CU may be split into one or multiple 8×8 PUs forprediction. Motion vectors are derived for each 8×8 PU and motioncompensation can be performed accordingly on the 8×8 PU. Under thetriangle prediction mode, a CU may be split into two triangular shapeprediction units. Motion vectors are derived for each PU and motioncompensation is performed accordingly. The triangle prediction mode issupported for inter prediction. More details of the triangle predictionmode are illustrated below.

Triangle Prediction Mode (or Triangular Partition Mode)

FIG. 6 is a schematic diagram illustrating splitting a CU intotriangular prediction units in accordance with some implementations ofthe present disclosure.

The concept of the triangle prediction mode is to introduce triangularpartitions for motion compensated prediction. The triangle predictionmode may also be named the triangular prediction unit mode (ortriangular partition mode). As shown in FIG. 6, a CU 602 or 604 is splitinto two triangular prediction units PU₁ and PU₂, in either the diagonalor the inverse diagonal direction (i.e., either splitting from top-leftcorner to bottom-right corner as shown in CU 602, or splitting fromtop-right corner to bottom-left corner as shown in CU 604). Eachtriangular prediction unit in the CU is inter-predicted using its ownuni-prediction motion vector and reference frame index which are derivedfrom a uni-prediction candidate list. An adaptive weighting process isperformed to the diagonal edge after predicting the triangularprediction units. Then, the transform and quantization process areapplied to the whole CU. It is noted that this mode is only applied to“skip” and “merge” modes in the current VVC. Although in FIG. 6, the CUis shown as a square block, the triangle prediction mode may be appliedto non-square (i.e. rectangular) shape CUs as well.

The uni-prediction candidate list may comprise one or more candidates,and each candidate may be a motion vector. Thus, throughout thisdisclosure, the terms “uni-prediction candidate list,” “uni-predictionmotion vector candidate list,” and “uni-prediction merge list” may beused interchangeably; and the terms “uni-prediction merge candidates”and “uni-prediction motion vectors” may also be used interchangeably.

Uni-Prediction Motion Vector Candidate List

FIG. 7 is a schematic diagram illustrating positions of the neighboringblocks in accordance with some implementations of the presentdisclosure.

In some examples, the uni-prediction motion vector candidate list mayinclude two to five uni-prediction motion vector candidates. In someother examples, other number may also be possible. It is derived fromneighboring blocks. The uni-prediction motion vector candidate list isderived from seven neighboring blocks including five spatial neighboringblocks (1 to 5) and two temporal co-located blocks (6 to 7), as shown inFIG. 7. The motion vectors of the seven neighboring blocks are collectedinto a first merge list. Then, a uni-prediction candidate list is formedbased on the first merge list motion vectors according to a specificorder. Based on the order, the uni-prediction motion vectors from thefirst merge list are put in the uni-prediction motion vector candidatelist first, followed by reference picture List 0 or L0 motion vector ofbi-prediction motion vectors, and then reference picture List 1 or L1motion vector of bi-prediction motion vectors, and then followed by theaveraged motion vector of the L0 and L1 motion vectors of bi-predictionmotion vectors. At that point, if the number of candidates is still lessthan a target number (which is five in the current VVC), zero motionvectors are added to the list to meet the target number.

A predictor is derived for each of the triangular PUs based on itsmotion vector. It is worth noting that the predictor derived covers alarger area than the actual triangular PU so that there is an overlappedarea of the two predictors along the shared diagonal edge of the twotriangular PUs. A weighting process is applied to the diagonal edge areabetween the two predictors to derive a final prediction for the CU. Theweighting factors currently used for the luminance and the chrominancesamples are {7/8, 6/8, 5/8, 4/8, 3/8, 2/8, 1/8} and {6/8, 4/8, 2/8},respectively.

Regular Merge Mode Motion Vector Candidate List

According to the current VVC, under the regular merge mode where a wholeCU is predicted without splitting into more than one PU, the motionvector candidate list or the merge candidate list is constructed using adifferent procedure than that for the triangle prediction mode.

Firstly, spatial motion vector candidates are selected based on motionvectors from neighboring blocks as indicated in FIG. 8, which is aschematic diagram illustrating positions of spatial merge candidates inaccordance with some implementations of the present disclosure. In thederivation of spatial merge candidates of a current block 802, a maximumof four merge candidates are selected among candidates that are locatedin positions as depicted in FIG. 8. The order of derivation isA₁→B₁→B₀→A₀→(B₂). The position B₂ is considered only when any PU ofpositions A₁, B₁, B₀, A₀ is not available or is intra coded.

Next, a temporal merge candidate is derived. In the derivation of thetemporal merge candidate, a scaled motion vector is derived based on theco-located PU belonging to the picture which has the smallest PictureOrder Count (POC) difference with the current picture within the givenreference picture list. The reference picture list to be used forderivation of the co-located PU is explicitly signaled in the sliceheader. The scaled motion vector for the temporal merge candidate isobtained as illustrated by the dotted line in FIG. 9 which illustratesmotion vector scaling for the temporal merge candidate in accordancewith some implementations of the present disclosure. The scaled motionvector for the temporal merge candidate is scaled from the motion vectorof the co-located PU col_PU using the POC distances, tb and td, where tbis defined to be the POC difference between the reference picture of thecurrent picture curr_ref and the current picture curr_pic and td isdefined to be the POC difference between the reference picture of theco-located picture col_ref and the co-located picture col_pic. Thereference picture index of the temporal merge candidate is set equal tozero. A practical realization of the scaling process is described in theHEVC draft specification. For a B-slice, two motion vectors, one forreference picture List 0 and the other for reference picture List 1, areobtained and combined to make the bi-predictive merge candidate.

FIG. 10 is a schematic diagram illustrating candidate positions for thetemporal merge candidate in accordance with some implementations of thepresent disclosure.

The position of co-located PU is selected between two candidatepositions, C3 and H, as depicted in FIG. 10. If the PU at position H isnot available, or is intra coded, or is outside of the current CTU,position C3 is used for the derivation of the temporal merge candidate.Otherwise, position H is used for the derivation of the temporal mergecandidate.

After inserting both spatial and temporal motion vectors into the mergecandidate list as described above, history-based merge candidates areadded. The so-called history-based merge candidates include those motionvectors from previously coded CUs, which are maintained in a separatemotion vector list, and managed based on certain rules.

After inserting history-based candidates, if the merge candidate list isnot full, pairwise average motion vector candidates are further addedinto the list. As its name indicates, this type of candidates isconstructed by averaging candidates already in the current list. Morespecifically, based on a certain order or rule, two candidates in themerge candidate list are taken each time and the average motion vectorof the two candidates is appended to the current list.

After inserting pairwise average motion vectors, if the merge candidatelist is still not full, zero motion vectors will be added to make thelist full.

Using Regular Merge List Construction Process to Construct a First MergeList for Triangle Prediction

The triangle prediction mode in the current VVC shares some similaritieswith the regular merge prediction mode, in its overall procedures informing a predictor. For example, under both prediction modes, a mergelist needs to be constructed based on at least the current CU'sneighboring spatial motion vectors and the co-located motion vectors. Atthe same time, the triangle prediction mode also has some aspects thatare different from the regular merge prediction mode.

For example, although a merge list needs to be constructed under boththe triangle prediction mode and the regular merge prediction mode, thedetailed procedures of obtaining such a list are different.

These differences incur additional cost to codec implementation asadditional logics are needed. The procedures and logics of obtaining amerge list may be unified and shared between the triangle predictionmode and the regular merge prediction mode.

In some examples, in forming the uni-directional prediction (also calleduni-prediction) merge list for the triangle prediction mode, beforeadding a new motion vector into the merge list, the new motion vector isfully pruned against those motion vectors already in the list. In otherwords, the new motion vector is compared with each motion vector that isalready in the uni-prediction merge list, and is added into the listonly when it is different from every motion vector in that merge list.Otherwise, the new motion vector is not added into the list.

According to some examples of the present disclosure, under the triangleprediction mode, the uni-directional prediction merge list isconstructed from the regular merge mode motion vector candidate list,which may be referred to as a regular merge list.

More specifically, to obtain a merge candidate list for the triangleprediction mode, a first merge list is firstly constructed based on themerge list construction process for the regular merge prediction. Thefirst merge list including a plurality of candidates, each being amotion vector. Then, the uni-directional prediction merge list for thetriangle prediction mode is further constructed using the motion vectorsin the first merge list.

It should be noted that the first merge list constructed in this casemay choose a different list size than that for the general merge mode orregular merge mode. In one example of the present disclosure, the firstmerge list has the same size as that for the general merge mode. Inanother example of the present disclosure, the first merge listconstructed has a list size different from that for the general mergemode.

Constructing Uni-Directional Prediction Merge List from the First MergeList

According to some examples of the present disclosure, theuni-directional prediction merge list for triangle prediction mode maybe constructed from the first merge list based on one of the followingmethods.

In an example of the present disclosure, to obtain the uni-directionalprediction merge list, prediction List 0 motion vectors of thecandidates in the first merge list are checked and selected into theuni-directional prediction merge list first. If the uni-directionalprediction merge list is not full (e.g., the number of candidates inthis list is still less than the target number) after this process,prediction List 1 motion vectors of the candidates in the first mergelist are checked and selected into the uni-directional prediction mergelist. If the uni-directional prediction merge list is still not full,prediction List 0 zero vectors are added into the uni-directionalprediction merge list. If the uni-directional prediction merge liststill not full, prediction List 1 zero vectors are added into theuni-directional prediction merge list.

In another example of the present disclosure, for each candidate in thefirst merge list, its prediction List 0 motion vector and predictionList 1 motion vector are added in an interleaving manner into theuni-directional prediction merge list. More specifically, for eachcandidate in the first merge list, if a candidate is a uni-directionalprediction motion vector, it is added directly into the uni-directionalprediction merge list. Otherwise, if the candidate is a bi-directionalprediction motion vector in the first merge list, its prediction List 0motion vector is first added into the uni-directional prediction mergelist, followed by its prediction List 1 motion vector. Once all motionvector candidates in the first merge list are checked and added, but theuni-directional prediction merge list is not full yet, uni-directionalprediction zero motion vectors may be added. For example, for eachreference frame index, a prediction List 0 zero motion vector and aprediction List 1 zero motion vector may be separately added into theuni-directional prediction merge list until the list is full.

In yet another example of the present disclosure, the uni-directionalprediction motion vectors from the first merge list are selected intothe uni-directional prediction merge list first. If the uni-directionalprediction merge list is not full after this process, for eachbi-directional prediction motion vectors in the first merge list, itsprediction List 0 motion vector is first added into the uni-directionalprediction merge list, followed by its prediction List 1 motion vector.After this process, if the uni-directional prediction merge list is notfull yet, uni-directional prediction zero motion vectors may be added.For example, for each reference frame index, a prediction List 0 zeromotion vector and a prediction List 1 zero motion vector may beseparately added into the uni-directional prediction merge list untilthe list is full.

In the descriptions above, when a uni-directional prediction motionvector is added into the uni-directional prediction merge list, a motionvector pruning process may be performed to make sure that the new motionvector to be added is different from those motion vectors already in theuni-directional prediction merge list. Such motion vector pruningprocess may also be performed in a partial manner for lower complexity,e.g., checking the new motion vector to be added only against some butnot all motion vectors already in the uni-directional prediction mergelist. In an extreme case, no motion vector pruning (i.e., motion vectorcomparison operation) is performed in the process.

Constructing Uni-Directional Prediction Merge List from the First MergeList Based on Picture Prediction Configuration

In some examples of the present disclosure, the uni-prediction mergelist may be constructed in an adaptive manner based on whether a currentpicture uses backward prediction. For example, the uni-prediction mergelist may be constructed using different methods depending on whether acurrent picture uses backward prediction. If the Picture Order Count(POC) values of all the reference pictures are not greater than thecurrent picture's POC value, it means that the current picture does notuse backward prediction.

In an example of the present disclosure, when a current picture does notuse backward prediction, or upon determining that the current picturedoes not use backward prediction, prediction List 0 motion vectors ofthe candidates in the first merge list are checked and selected into theuni-directional prediction merge list first, followed by prediction List1 motion vectors of those candidates; and if the uni-directionalprediction merge list is still not full, uni-prediction zero motionvectors may be added. Otherwise, if the current picture uses backwardprediction, prediction List 0 and List 1 motion vectors of eachcandidate in the first merge list may be checked and selected into theuni-directional prediction merge list in an interleaving manner asdescribed above, i.e., the prediction List 0 motion vector of the firstcandidate in the first merge list is added, followed by the predictionList 1 motion vector of the first candidate, and then the predictionList 0 motion vector of the second candidate is added, followed by theprediction List 1 motion vector of the second candidate, and so on. Atthe end of the process, if the uni-directional prediction merge list isstill not full, uni-prediction zero vectors may be added.

In another example of the present disclosure, if a current picture doesnot use backward prediction, prediction List 1 motion vectors of thecandidates in the first merge list are checked and selected into theuni-directional prediction merge list first, followed by prediction List0 motion vectors of those candidates; and if the uni-directionalprediction merge list is still not full, uni-prediction zero motionvectors may be added. Otherwise, if the current picture uses backwardprediction, prediction List 0 and List 1 motion vectors of eachcandidate in the first merge list may be checked and selected into theuni-directional prediction merge list in an interleaving manner asdescribed above, i.e., the prediction List 0 motion vector of the firstcandidate in the first merge list is added, followed by the predictionList 1 motion vector of the first candidate, and then the predictionList 0 motion vector of the second candidate is added, followed by theprediction List 1 motion vector of the second candidate, and so on. Atthe end of the process, if the uni-directional prediction merge list isstill not full, uni-prediction zero vectors may be added.

In yet another example of the present disclosure, if a current picturedoes not use backward prediction, only prediction List 0 motion vectorsof the candidates in the first merge list are checked and selected intothe uni-directional prediction merge list first, and if theuni-directional prediction merge list is still not full, uni-predictionzero motion vectors may be added. Otherwise, if the current picture usesbackward prediction, prediction List 0 and List 1 motion vectors of eachcandidate in the first merge list may be checked and selected into theuni-directional prediction merge list in an interleaving manner asdescribed above, i.e., the prediction List 0 motion vector of the firstcandidate in the first merge list is added, followed by the predictionList 1 motion vector of the first candidate, and then the predictionList 0 motion vector of the second candidate is added, followed by theprediction List 1 motion vector of the second candidate, and so on. Atthe end of the process, if the uni-directional prediction merge list isstill not full, uni-prediction zero vectors may be added.

In still another example of the present disclosure, if a current picturedoes not use backward prediction, only prediction List 1 motion vectorsof the candidates in the first merge list are checked and selected intothe uni-directional prediction merge list first, and if theuni-directional prediction merge list is still not full, uni-predictionzero motion vectors may be added. Otherwise, if the current picture usesbackward prediction, prediction List 0 and List 1 motion vectors of eachcandidate in the first merge list may be checked and selected into theuni-directional prediction merge list in an interleaving manner asdescribed above, i.e., the prediction List 0 motion vector of the firstcandidate in the first merge list is added, followed by the predictionList 1 motion vector of the first candidate, and then the predictionList 0 motion vector of the second candidate is added, followed by theprediction List 1 motion vector of the second candidate, and so on. Atthe end of the process, if the uni-directional prediction merge list isstill not full, uni-prediction zero vectors may be added.

Using the First Merge List for Triangle Prediction without CreatingUni-Directional Prediction Merge List

In the above examples, a uni-directional prediction merge list fortriangle prediction is constructed by selecting motion vectors from thefirst merge list into the uni-directional prediction merge list.However, in practice, the methods may be implemented in different ways,with or without the uni-directional prediction (or uni-prediction) mergelist being physically formed. In some examples, the first merge list maybe used directly without physically creating a uni-directionalprediction merge list. For example, the List 0 and/or List 1 motionvectors of each candidate in the first merge list may be simply indexedbased on a certain order and accessed directly from the first mergelist.

In one example, the first merge list may be obtained from a decoder orother electronic devices/components. In other examples, afterconstructing the first merge list which includes a plurality ofcandidates, each being one or more motion vectors, based on a merge listconstruction process for regular merge prediction, a uni-directionalprediction merge list is not constructed, but instead, an index listingincluding a plurality of reference indices, each reference index being areference to a motion vector of a candidate in the first merge list, isconstructed. This index listing is used for the triangle predictionmode. The index listing may be considered as a representation of auni-directional prediction merge list for the triangular prediction, andthe uni-directional prediction merge list includes at least a subset ofcandidates in the first merge list corresponding to the referenceindices. It should be noted that an order of indexing may follow any ofthe selecting orders described in the examples in which auni-directional prediction merge list is constructed. In practice, suchindex listing may be implemented in different manners. For example, itmay be implemented as a list explicitly. In other examples, it may alsobe implemented or obtained in certain logics and/or program functionswithout explicitly forming any list.

In some examples of the present disclosure, the index listing may beconstructed in an adaptive manner based on whether a current pictureuses backward prediction. For example, the reference indices in theindex listing may be arranged depending on whether a current pictureuses backward prediction, i.e., based on a comparison result of aPicture Order Count (POC) of a current picture and POCs of referencepictures. If the Picture Order Count (POC) values of all the referencepictures are not greater than the current picture's POC value, it meansthat the current picture does not use backward prediction.

In one example of the present disclosure, when a current picture doesnot use backward prediction, prediction List 0 motion vectors of thecandidates in the first merge list are used as the uni-directionalprediction merge candidates, indexed according to the same index orderas they are in the first merge list. That is, upon determining that thePOC of the current picture is greater than each one of the POCs of thereference pictures, the reference indices are arranged according to asame order of List 0 motion vectors of the candidates in the first mergelist. Otherwise, if the current picture uses backward prediction, List 0and List 1 motion vectors of each candidate in the first merge list areused as the uni-directional prediction merge candidates, indexed basedon an interleaving manner, i.e., List 0 motion vector of the firstcandidate in the first merge list followed by List 1 motion vector ofthe first candidate, and then List 0 motion vector of the secondcandidate followed by List 1 motion vector of the second candidate, andso on. That is, upon determining that the POC of the current picture issmaller than at least one of the POCs of the reference pictures, thereference indices are arranged according to an interleaving manner ofList 0 and List 1 motion vectors of each candidate in the first mergelist, where the candidate is a bi-directional prediction motion vector.In the case where a candidate in the first merge list is auni-directional motion vector, a zero motion vector is indexed as theuni-directional prediction merge candidate following the motion vectorof that candidate. This ensures that for the case where the currentpicture uses backward prediction, each candidate in the first mergelist, regardless it is a bi-directional or uni-directional predictionmotion vector, provides two uni-directional motion vectors as theuni-directional prediction merge candidates.

In another example of the present disclosure, when a current picturedoes not use backward prediction, prediction List 0 motion vectors ofthe candidates in the first merge list are used as the uni-directionalprediction merge candidates, indexed according to the same index orderas they are in the first merge list. Otherwise, if the current pictureuses backward prediction, List 0 and List 1 motion vectors of eachcandidate in the first merge list are used as the uni-directionalprediction merge candidates, indexed based on an interleaving manner asdescribed above, i.e., List 0 motion vector of the first candidate inthe first merge list followed by List 1 motion vector of the firstcandidate, and then List 0 motion vector of the second candidatefollowed by list 1 motion vector of the second candidate, and so on. Inthe case where a candidate in the first merge list is a uni-directionalmotion vector, the motion vector plus certain motion offset is indexedas the uni-directional prediction merge candidate following the motionvector of the candidate.

Thus, in the case where a candidate in the first merge list is auni-directional motion vector, upon determining that the POC of thecurrent picture is smaller than at least one of the POCs of thereference pictures, the reference indices are arranged according to aninterleaving manner of: a motion vector of each candidate in the firstmerge list, and a zero motion vector, or the motion vector plus anoffset.

In the above processes, when checking a new motion vector to be addedinto the uni-directional prediction merge list, pruning may be performedfully, or partially. When it is performed partially, it means that thenew motion vector is compared against some, but not all, of the motionvectors that are already in the uni-prediction merge list. In an extremecase, no motion vector pruning (i.e. motion vector comparison operation)is performed in the process.

The motion vector pruning may also be performed adaptively in formingthe uni-prediction merge list, based on whether the current picture usesbackward prediction or not. For example, for the examples of the presentdisclosure relating to index listing determination based on pictureprediction configuration, when the current picture does not use backwardprediction, motion vector pruning operation is performed, either fullyor partially. When the current picture uses backward prediction, motionvector pruning operation is not performed.

Selecting Uni-Prediction Merge Candidates for Triangle Prediction Mode

In addition to the abovementioned examples, other ways of uni-predictionmerge list construction or uni-prediction merge candidate selection aredisclosed.

In one example of the present disclosure, once the first merge list forthe regular merge mode is constructed, uni-prediction merge candidatesmay be selected for triangle prediction according to the followingrules:

for a motion vector candidate in the first merge list, one and only oneof its List 0 or List 1 motion vector is used for triangle prediction;

for a given motion vector candidate in the first merge list, if itsmerge index value in the list is an even number, its List 0 motionvector is used for triangle prediction if it is available, and in thecase that this motion vector candidate does not have a List 1 motionvector, its List 0 motion vector is used for triangle prediction; and

for a given motion vector candidate in the first merge list, if itsmerge index value in the list is an odd number, its List 1 motion vectoris used for triangle prediction if it is available, and in the case thatthis motion vector candidate does not have a List 1 motion vector, itsList 0 motion vector is used for triangle prediction.

FIG. 11A shows an example of uni-prediction motion vector (MV) selection(or uni-prediction merge candidate selection) for triangle predictionmode. In the example, the first 5 merge MV candidates derived in thefirst merge list are indexed from 0 to 4; and each row has two columns,representing the List 0 and the List 1 motion vector respectively for acandidate in the first merge list. Each candidate in the list may beeither uni-predicted or bi-predicted. For a uni-predicted candidate, ithas only a List 0 or a List 1 motion vector, but not both. For abi-predicted candidate, it has both List 0 and List 1 motion vectors. InFIG. 11A, for each merge index, the motion vectors marked with “x” arethose motion vectors to be used first for triangle prediction if theyare available. If a motion vector marked in “x” is not available, theunmarked motion vector corresponding to the same merge index is then tobe used for triangle prediction.

The above concept may be extended to other examples. FIG. 11B showsanother example of uni-prediction motion vector (MV) selection fortriangle prediction mode. According to FIG. 11B, the rules for selectinguni-prediction merge candidates for triangle prediction are as follows:

for a motion vector candidate in the first merge list, one and only oneof its List 0 or List 1 motion vector is used for triangle prediction;

for a given motion vector candidate in the first merge list, if itsmerge index value in the list is an even number, its List 1 motionvector is used for triangle prediction if it is available, and in thecase that this motion vector candidate does not have a List 1 motionvector, its List 0 motion vector is used for triangle prediction; and

for a given motion vector candidate in the first merge list, if itsmerge index value in the list is an odd number, its List 0 motion vectoris used for triangle prediction if it is available, and in the case thatthis motion vector candidate does not have a List 0 motion vector, itsList 1 motion vector is used for triangle prediction.

In some examples, other different orders may be defined and used forselecting uni-prediction merge candidates for triangle prediction fromthose motion vector candidates in the first merge list. Morespecifically, for a given motion vector candidate in the first mergelist, the decision of whether its List 0 or List 1 motion vector is usedfirst when available for triangle prediction does not have to bedependent on the parity of the candidate's index value in the firstmerge list as described above. For examples, the following rules mayalso be used:

for a motion vector candidate in the first merge list, one and only oneof its List 0 or List 1 motion vector is used for triangle prediction;

based on a certain pre-defined pattern, for a number of motion vectorcandidates in the first merge list, their List 0 motion vector are usedfor triangle prediction if available, and in the case that a List 0motion vector does not exist, the corresponding List 1 motion vector isused for triangle prediction; and

based on the same pre-defined pattern, for the remaining motion vectorcandidates in the first merge list, their List 1 motion vector are usedfor triangle prediction if available, and in the case that a List 1motion vector does not exist, the corresponding List 0 motion vector isused for triangle prediction.

FIGS. 12A to 12D show some examples of the pre-defined patterns inuni-prediction motion vector (MV) selection for triangle predictionmode. For each merge index, the motion vectors marked with “x” are thosemotion vectors used first for triangle prediction if they are available.If a motion vector marked in “x” is not available, the unmarked motionvector corresponding to the same merge index is then used for triangleprediction.

In FIG. 12A, for the first three motion vector candidates in the firstmerge list, their List 0 motion vectors are checked first. Only when aList 0 motion vector is not available, the corresponding List 1 motionvector is used for triangle prediction. For the fourth and fifth motionvector candidates in the first merge list, their List 1 motion vectorsare checked first. Only when a List 1 motion vector is not available,the corresponding List 0 motion vector is used for triangle prediction.FIGS. 12B to 12D show three other patterns in selecting uni-predictionmerge candidates from the first merge list. The examples shown in thefigures are not limiting, and there exist further examples. Forinstance, the horizontally and/or vertically mirrored versions of thosepatterns shown in FIGS. 12A to 12D may also be used.

The selected uni-prediction merge candidates may be indexed and accesseddirectly from the first merge list; or these selected uni-predictionmerge candidates may be put into a uni-prediction merge list fortriangle prediction. The constructed uni-prediction merge list includesa plurality of uni-prediction merge candidates, and each uni-predictionmerge candidate includes one motion vector of a corresponding candidatein the first merge list. According to some examples of the presentdisclosure, each candidate in the first merge list includes at least oneof a List 0 motion vector and a List 1 motion vector, and eachuni-prediction merge candidate may be a single one of the List 0 andList 1 motion vectors of the corresponding candidate in the first mergelist. Each uni-prediction merge candidate is associated with a mergeindex of integer value; and the List 0 and List 1 motion vectors areselected based on a preset rule for the uni-prediction merge candidates.

In one example, for each uni-prediction merge candidate having an evenmerge index value, a List 0 motion vector of the corresponding candidatein the first merge list is selected as the uni-prediction mergecandidate; and for each uni-prediction merge candidate having an oddmerge index value, a List 1 motion vector of the corresponding candidatein the first merge list is selected. In another example, for eachuni-prediction merge candidate having an even merge index value, a List1 motion vector of the corresponding candidate in the first merge listis selected; and for each uni-prediction merge candidate having an oddmerge index value, a List 0 motion vector of the corresponding candidatein the first merge list is selected.

In yet another example, for each uni-prediction merge candidate, a List1 motion vector of the corresponding candidate in the first merge listis selected as the uni-prediction merge candidate, upon determining thatthe List 1 motion vector is available; and a List 0 motion vector of thecorresponding candidate in the first merge list is selected upondetermining that the List 1 motion vector is not available.

In still another example, for each uni-prediction merge candidate havinga merge index value within a first range, a List 0 motion vector of thecorresponding candidate in the first merge list is selected as theuni-prediction merge candidate; and for each uni-prediction mergecandidate having a merge index value within a second range, a List 1motion vector of the corresponding candidate in the first merge list isselected.

In the above processes, motion vector pruning may be performed as well.Such pruning may be done fully, or partially. When it is performedpartially, it means a new motion vector is compared against some, butnot all, of the motion vectors that are already in the uni-predictionmerge list. It may also mean that only some, but not all, new motionvectors need to be checked for pruning before used as merge candidatesfor triangle prediction. One specific example is that only the secondmotion vector is checked against the first motion vector for pruningbefore it is used as a merge candidate for triangle prediction, whileall other motion vectors are not checked for pruning. In the extremecase, no motion vector pruning (i.e. motion vector comparison operation)is performed in the process.

Although the methods of forming a uni-prediction merge list in thisdisclosure are described with respect to triangle prediction mode, thesemethods are applicable to other prediction modes of similar kinds. Forexample, under the more general geometric partition prediction modewherein a CU is partitioned into two PUs along a line not exactlydiagonal, the two PUs may have a geometric shape such as triangle,wedge, or trapezoid shapes. In such cases, prediction of each PU isformed in a similar manner as in the triangle prediction mode, themethods described herein are equally applicable.

FIG. 13 is a block diagram illustrating an apparatus for video coding inaccordance with some implementations of the present disclosure. Theapparatus 1300 may be a terminal, such as a mobile phone, a tabletcomputer, a digital broadcast terminal, a tablet device, or a personaldigital assistant.

As shown in FIG. 13, the apparatus 1300 may include one or more of thefollowing components: a processing component 1302, a memory 1304, apower supply component 1306, a multimedia component 1308, an audiocomponent 1310, an input/output (I/O) interface 1312, a sensor component1314, and a communication component 1316.

The processing component 1302 usually controls overall operations of theapparatus 1300, such as operations relating to display, a telephonecall, data communication, a camera operation and a recording operation.The processing component 1302 may include one or more processors 1320for executing instructions to complete all or a part of steps of theabove method. Further, the processing component 1302 may include one ormore modules to facilitate interaction between the processing component1302 and other components. For example, the processing component 1302may include a multimedia module to facilitate the interaction betweenthe multimedia component 1308 and the processing component 1302.

The memory 1304 is configured to store different types of data tosupport operations of the apparatus 1300. Examples of such data includeinstructions, contact data, phonebook data, messages, pictures, videos,and so on for any application or method that operates on the apparatus1300. The memory 1304 may be implemented by any type of volatile ornon-volatile storage devices or a combination thereof, and the memory1304 may be a Static Random Access Memory (SRAM), an ElectricallyErasable Programmable Read-Only Memory (EEPROM), an ErasableProgrammable Read-Only Memory (EPROM), a Programmable Read-Only Memory(PROM), a Read-Only Memory (ROM), a magnetic memory, a flash memory, amagnetic disk or a compact disk.

The power supply component 1306 supplies power for different componentsof the apparatus 1300. The power supply component 1306 may include apower supply management system, one or more power supplies, and othercomponents associated with generating, managing and distributing powerfor the apparatus 1300.

The multimedia component 1308 includes a screen providing an outputinterface between the apparatus 1300 and a user. In some examples, thescreen may include a Liquid Crystal Display (LCD) and a Touch Panel(TP). If the screen includes a touch panel, the screen may beimplemented as a touch screen receiving an input signal from a user. Thetouch panel may include one or more touch sensors for sensing a touch, aslide and a gesture on the touch panel. The touch sensor may not onlysense a boundary of a touching or sliding actions, but also detectduration and pressure related to the touching or sliding operation. Insome examples, the multimedia component 1308 may include a front cameraand/or a rear camera. When the apparatus 1300 is in an operation mode,such as a shooting mode or a video mode, the front camera and/or therear camera may receive external multimedia data.

The audio component 1310 is configured to output and/or input an audiosignal. For example, the audio component 1310 includes a microphone(MIC). When the apparatus 1300 is in an operating mode, such as a callmode, a recording mode and a voice recognition mode, the microphone isconfigured to receive an external audio signal. The received audiosignal may be further stored in the memory 1304 or sent via thecommunication component 1316. In some examples, the audio component 1310further includes a speaker for outputting an audio signal.

The I/O interface 1312 provides an interface between the processingcomponent 1302 and a peripheral interface module. The above peripheralinterface module may be a keyboard, a click wheel, a button, or thelike. These buttons may include but not limited to, a home button, avolume button, a start button and a lock button.

The sensor component 1314 includes one or more sensors for providing astate assessment in different aspects for the apparatus 1300. Forexample, the sensor component 1314 may detect an on/off state of theapparatus 1300 and relative locations of components. For example, thecomponents are a display and a keypad of the apparatus 1300. The sensorcomponent 1314 may also detect a position change of the apparatus 1300or a component of the apparatus 1300, presence or absence of a contactof a user on the apparatus 1300, an orientation oracceleration/deceleration of the apparatus 1300, and a temperaturechange of apparatus 1300. The sensor component 1314 may include aproximity sensor configured to detect presence of a nearby objectwithout any physical touch. The sensor component 1314 may furtherinclude an optical sensor, such as a CMOS or CCD image sensor used in animaging application. In some examples, the sensor component 1314 mayfurther include an acceleration sensor, a gyroscope sensor, a magneticsensor, a pressure sensor, or a temperature sensor.

The communication component 1316 is configured to facilitate wired orwireless communication between the apparatus 1300 and other devices. Theapparatus 1300 may access a wireless network based on a communicationstandard, such as WiFi, 4G, or a combination thereof. In an example, thecommunication component 1316 receives a broadcast signal or broadcastrelated information from an external broadcast management system via abroadcast channel. In an example, the communication component 1316 mayfurther include a Near Field Communication (NFC) module for promotingshort-range communication. For example, the NFC module may beimplemented based on Radio Frequency Identification (RFID) technology,infrared data association (IrDA) technology, Ultra-Wide Band (UWB)technology, Bluetooth (BT) technology and other technology.

In an example, the apparatus 1300 may be implemented by one or more ofApplication Specific Integrated Circuits (ASIC), Digital SignalProcessors (DSP), Digital Signal Processing Devices (DSPD), ProgrammableLogic Devices (PLD), Field Programmable Gate Arrays (FPGA), controllers,microcontrollers, microprocessors or other electronic elements toperform the above method.

A non-transitory computer readable storage medium may be, for example, aHard Disk Drive (HDD), a Solid-State Drive (SSD), Flash memory, a HybridDrive or Solid-State Hybrid Drive (SSHD), a Read-Only Memory (ROM), aCompact Disc Read-Only Memory (CD-ROM), a magnetic tape, a floppy diskand etc.

FIG. 14 is a flowchart illustrating an exemplary process of video codingfor motion compensated prediction using triangular prediction unit inaccordance with some implementations of the present disclosure.

In step 1402, the processor 1320 partitions video pictures into aplurality of coding units (CUs), at least one of which is furtherpartitioned into two prediction units (PUs) including at least onetriangular shaped PU. In other examples, the two PUs may include a pairof triangular shaped PUs, a pair of wedge shaped PUs, or other geometricshaped PUs.

In step 1404, the processor 1320 constructs a first merge list includinga plurality of candidates, each including one or more motion vectors,based on a merge list construction process for regular merge prediction.

In step 1406, the processor 1320 obtains an index listing including aplurality of reference indices, where each reference index includes areference to a motion vector of a candidate in the first merge list.

In some examples, there is provided an apparatus for video coding. Theapparatus includes a processor 1320; and a memory 1304 configured tostore instructions executable by the processor; where the processor,upon execution of the instructions, is configured to perform a method asillustrated in FIG. 14.

In some other examples, there is provided a non-transitory computerreadable storage medium 1304, having instructions stored therein. Whenthe instructions are executed by a processor 1320, the instructionscause the processor to perform a method as illustrated in FIG. 14.

The description of the present disclosure has been presented forpurposes of illustration, and is not intended to be exhaustive orlimited to the present disclosure. Many modifications, variations, andalternative implementations will be apparent to those of ordinary skillin the art having the benefit of the teachings presented in theforegoing descriptions and the associated drawings.

The examples were chosen and described in order to explain theprinciples of the disclosure, and to enable others skilled in the art tounderstand the disclosure for various implementations and to bestutilize the underlying principles and various implementations withvarious modifications as are suited to the particular use contemplated.Therefore, it is to be understood that the scope of the disclosure isnot to be limited to the specific examples of the implementationsdisclosed and that modifications and other implementations are intendedto be included within the scope of the present disclosure.

What is claimed is:
 1. A method for video coding, comprising:partitioning video pictures into a plurality of coding units (CUs), atleast one of which is further portioned into two prediction units (PUs)including at least one triangular shaped PU; constructing a first mergelist comprising a plurality of candidates, each comprising one or moremotion vectors, based on a merge list construction process for regularmerge prediction; and obtaining an index listing comprising a pluralityof reference indices, wherein each reference index comprises a referenceto a motion vector of a candidate in the first merge list.
 2. The methodof claim 1, wherein the index listing is a representation of auni-directional prediction merge list for the triangular shaped PU, andthe uni-directional prediction merge list comprises at least a subset ofcandidates in the first merge list corresponding to the referenceindices.
 3. The method of claim 1, further comprising: determining acomparison result of a Picture Order Count (POC) of a current pictureand POCs of reference pictures, wherein the reference indices in theindex listing are arranged according to a preset order, based on thecomparison result.
 4. The method of claim 3, wherein, upon determiningthat the POC of the current picture is greater than each one of the POCsof the reference pictures, the reference indices are arranged accordingto a same order of corresponding motion vectors, or List 0 motionvectors, of the candidates in the first merge list.
 5. The method ofclaim 3, wherein, upon determining that the POC of the current pictureis smaller than at least one of the POCs of the reference pictures, thereference indices are arranged according to an interleaving manner ofList 0 and List 1 motion vectors of each candidate in the first mergelist, where the candidate is a bi-directional prediction motion vector.6. The method of claim 3, wherein, upon determining that the POC of thecurrent picture is smaller than at least one of the POCs of thereference pictures, the reference indices are arranged according to aninterleaving manner of: a motion vector of each candidate in the firstmerge list, and a zero motion vector, or the motion vector plus anoffset, where the candidate is a uni-directional prediction motionvector.
 7. An apparatus for video coding, comprising: one or moreprocessors; and a memory configured to store instructions executable bythe one or more processors; wherein the one or more processors, uponexecution of the instructions, are configured to: partition videopictures into a plurality of coding units (CUs), at least one of whichis further portioned into two prediction units (PUs) including at leastone triangular shaped PU; construct a first merge list comprising aplurality of candidates, each comprising one or more motion vectors,based on a merge list construction process for regular merge prediction;and obtain an index listing comprising a plurality of reference indices,wherein each reference index comprises a reference to a motion vector ofa candidate in the first merge list.
 8. The apparatus of claim 7,wherein the index listing is a representation of a uni-directionalprediction merge list for the triangular shaped PU, and theuni-directional prediction merge list comprises at least a subset ofcandidates in the first merge list corresponding to the referenceindices.
 9. The apparatus of claim 7, wherein the processor is furtherconfigured to: determine a comparison result of a Picture Order Count(POC) of a current picture and POCs of reference pictures, wherein thereference indices in the index listing are arranged according to apreset order, based on the comparison result.
 10. The apparatus of claim9, wherein, upon determining that the POC of the current picture isgreater than each one of the POCs of the reference pictures, thereference indices are arranged according to a same order ofcorresponding motion vectors, or List 0 motion vectors, of thecandidates in the first merge list.
 11. The apparatus of claim 9,wherein, upon determining that the POC of the current picture is smallerthan at least one of the POCs of the reference pictures, the referenceindices are arranged according to an interleaving manner of List 0 andList 1 motion vectors of each candidate in the first merge list, wherethe candidate is a bi-directional prediction motion vector.
 12. Theapparatus of claim 9, wherein, upon determining that the POC of thecurrent picture is smaller than at least one of the POCs of thereference pictures, the reference indices are arranged according to aninterleaving manner of: a motion vector of each candidate in the firstmerge list, and a zero motion vector, or the motion vector plus anoffset, where the candidate is a uni-directional prediction motionvector.
 13. A non-transitory computer readable storage medium,comprising instructions stored therein, wherein, upon execution of theinstructions by one or more processors, the instructions cause the oneor more processors to perform acts comprising: partitioning videopictures into a plurality of coding units (CUs), at least one of whichis further portioned into two prediction units (PUs) including at leastone triangular shaped PU; constructing a first merge list comprising aplurality of candidates, each comprising one or more motion vectors,based on a merge list construction process for regular merge prediction;and obtaining an index listing comprising a plurality of referenceindices, wherein each reference index comprises a reference to a motionvector of a candidate in the first merge list.
 14. The non-transitorycomputer readable storage medium of claim 13, wherein the index listingis a representation of a uni-directional prediction merge list for thetriangular shaped PU, the uni-directional prediction merge listcomprises at least a subset of candidates in the first merge listcorresponding to the reference indices.
 15. The non-transitory computerreadable storage medium of claim 13, wherein the instructions furthercause the processor to: determine a comparison result of a Picture OrderCount (POC) of a current picture and POCs of reference pictures, whereinthe reference indices in the index listing are arranged according to apreset order, based on the comparison result.
 16. The non-transitorycomputer readable storage medium of claim 15, wherein, upon determiningthat the POC of the current picture is greater than each one of the POCsof the reference pictures, the reference indices are arranged accordingto a same order of corresponding motion vectors, or List 0 motionvectors, of the candidates in the first merge list.
 17. Thenon-transitory computer readable storage medium of claim 15, wherein,upon determining that the POC of the current picture is smaller than atleast one of the POCs of the reference pictures, the reference indicesare arranged according to an interleaving manner of List 0 and List 1motion vectors of each candidate in the first merge list, where thecandidate is a bi-directional prediction motion vector.
 18. Thenon-transitory computer readable storage medium of claim 15, wherein,upon determining that the POC of the current picture is smaller than atleast one of the POCs of the reference pictures, the reference indicesare arranged according to an interleaving manner of: a motion vector ofeach candidate in the first merge list, and a zero motion vector, or themotion vector plus an offset, where the candidate is a uni-directionalprediction motion vector.